The present invention relates to supply circuits for fluids under pressure, and particularly to assemblies in such circuits to eliminate or substantially minimise over-pressures resulting from sudden interruptions in the flow of a gaseous fluid in the circuit in any process in which the pressure of the fluid in question is regulated cyclically by an obturator which employs all-or-nothing operation, such as an electrical valve of the kind which are found particularly in gas-fired reheating furnaces.
Conventional reheating furnaces are fed with gas at a constant pressure by means of regulator and pressure-reducer which is a pneumatically operated device which works in an independent fashion by taking energy directly from the gas in the supply pipe, which latter will hereinafter be referred to as "the main pipe".
However, the heating members and their safety devices for their part are electrically operated. In particular, the gas-flow valve is an electrical valve which opens and closes fully and rapidly in a cyclic fashion.
This electrical valve therefore employs very high-speed all-or-nothing operation, taking only a few hundredths of a second to open or close, whereas the regulator and gas-pressure reducer usually has a response time of the order of a second or half a second when carrying out the same operation.
Consequently, when the electrical valve closes, the gas continues to flow in the part of the main pipe between the regulator and pressure-reducer and the said electrical valve for the length of time which the regulator and pressure-reducer takes to close fully.
This excess quantity of gas gives rise to an over-pressure which often exceeds the .+-. 15% usually fixed as a maximum to ensure proper combustion and over-pressure therefore triggers the burner's safety device and holds it out. It would only be held out temporarily and the installation could be put back into operation if the over-pressure downstream of the regulator and pressure-reducer were not maintained. However, if the installation is properly built it allows no means of escape. Consequently, the over-pressure is maintained and it is therefore necessary to take manual action to put the installation back into operation. When the electrical valve opens similar phenomena occur but in the opposite direction.
It was thought that this drawback could be overcome by fitting a valve to the main pipe to release the excess gas. However, even apart from the fact that this solution, which involves the loss of gas, is not very acceptable from an economic point of view, it is also normally not very suitable from a technical point of view because of the long response time of the valve in question.
It is an object of the present invention to remove or reduce these differences in the duration and level of pressures in such a way that installations can operate normally, with their safety devices functioning in the normal way and without the maximum pressure limits of .+-. 15% which have to be observed for proper combustion being exceeded.
Another object of the invention is to provide an assembly which may easily be fitted to gas pipes equipped with a conventional regulator and pressure-reducer electrical valve combination with the minimum of expense, and which operates in such a way as to meet the conditions mentioned without requiring manual intervention.